let rec hello_worlds n = function
    | 0 -> ()
    | n -> print_endline "Hello World";
        pred n
        |> hello_worlds
let main =
    input_line stdin
    |> int_of_string
    |> hello_worlds

File "solution.ml", line 5, characters 8-38:
Error: This expression has type int -> unit
       but an expression was expected of type unit